Some determinant factors underlying several manifestations of filarial disease have recently been clarified; chronic lymphedema and elephantiasis have been produced by filarial infection and the basic lesions have been studied grossly radiologically and histologically. Host-parasite relationships in less bizarre syndromes such as episodic filarial fever, chylous reflux (chyluria, chylous thorax, chylous ascites, etc.) and cryptic filariasis (TPE, E.L., etc.) are less clear. (1) Chylous reflux will be studied in cats using B. pahangi larvae inoculated into defined anatomical locations. (2) Episodic fever will be studied in cats hyperinfected with low doses of Brugia. (3) The effect of heterologous (non-maturing) larvae on later inoculations of a "normal" parasite will be assessed using Dirofilaria repens/B. pahangi in syngeneic rats. Parasitological, hematological and some immunological parameters will be established. (4) Double infections with no niche competition will be assessed using Brugia/Dirofilaria in cats. (5) Syngeneic rat strains will be assessed for their receptivity a/o response to B. pahangi in order for study of variances in genetically based host responses. (6) Studies on intra-specific morphological variability will be continued to afford more precise definition of parasites and to seek diagnostic criteria in zoonotic filarial disease.